Christopher is 51 years old and Vanessa is 6 years old. How many years will it take until Christopher is only 4 times as old as Vanessa?
We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Christopher will be $51 + y$ years old and Vanessa will be $6 + y$ years old. At that time, Christopher will be 4 times as old as Vanessa. Writing this information as an equation, we get: $51 + y = 4 (6 + y)$ Simplifying the right side of this equation, we get: $51 + y = 24 + 4 y$ Solving for $y$ , we get: $3 y = 27$ $y = 9$.